Cohort studies are descriptive studies that describe the incidence of outcomes over time. They are also analytic studies in that they help to determine the causal relationships between outcomes and explanatory factors. Explanatory factors can be either risk and/or prognostic factors.

These studies are expensive and take time so diseases to be studied should not be too rare (use case-control method). Or, the disease should have a high attributable risk.

Attributable risk is the difference between 2 proportions. It quantifies the number of occurrences of a health outcome that is due to, or can be attributed to, the exposure or risk factor. It is used to assess the impact of eliminating a risk factor.